The present invention relates to a steering wheel comprising a one piece hub for fastening of the steering wheel on a steering column.
Such steering wheels are currently produced by casting from aluminum- or magnesium alloys and are provided with a casing of plastic. Since, in modern vehicles, the steering column for safety reasons has an end spaced from a plane defined by the steering wheel rim, the steering wheel spokes run in a funnel shape from the steering wheel rim to the steering wheel hub, which is structured for fastening on the steering column. A type of fastening which has proved successful for decades and is used in numerous vehicle series is characterized in that the hub of the steering wheel is placed onto the end of the steering column and is tensioned by means of a nut screwed on the end face onto the steering column against a tapered abutment face on the steering column. This connection is generally supplemented by a spline connection.
When the steering wheel is equipped with an inflatable airbag, this type of connection of the steering wheel with the steering column is only possible if the airbag module can be installed after the steering wheel has been mounted on the steering column. This installation sequence is undesired, because it delays the final installation of the vehicle and because the fastening of the airbag module in the steering wheel must be structurally coordinated therewith, whichxe2x80x94compared with a pre-installation of the airbag module in the steering wheelxe2x80x94is more costly and more complicated. One has therefore endeavored for a long time to present possibilities in which the steering wheel together with the incorporated airbag module can be supplied for final installation and can be fastened on the steering column. If screws are used which extend parallel to the steering column and are inserted from the rear face of the steering wheel, the installation is made very difficult, because the space behind the steering wheel is only accessible with difficulty in many vehicles. If one or more fastening screws are arranged radially to the steering wheel column, further fastening elements are necessary in order to be able to secure the steering wheel axially to the steering column and to provide a reliable connection for the transmission of the steering forces. The handling of additional fastening elements is complicated and still requires too much time in the final installation, which for economic reasons is to be as short as possible.
From the German Utility Model 297 22 825 a steering wheel is known in which the hub region is divided by slits arranged parallel to the steering column axis into hub sections which are able to be tensioned radially with respect to each other. After the steering wheel has been placed onto the steering column and both parts are aligned with each other in the appropriate position, bracing takes place by a screw which is arranged tangentially to the bore in the steering wheel hub to press the hub sections of the steering wheel hub against the shaft of the steering column, and the screw engages tangentially into an encircling groove on the steering column to ensure axial attachment of the steering wheel on the steering column. Thereby, all the requirements with regard to short final installation times and a structurally simplified structural unit of the steering wheel and airbag module can be realized, without restrictions having to be taken into account with regard to safety and reliability of the fastening of the steering wheel on the steering column.
The hub sections devided by slits can only be tensioned with respect to each other by means of a tangentially arranged tightening screw when they have through-bores and are arranged between an external nut and the head of the tightening screw. As a separate nut is undesired in the final installation, the necessary thread in the known steering wheel is arranged in one of the two hub sections, and the other hub section is provided with a through-bore and a stop for the screw head.
In the event of dismounting of the steering wheel from the steering column, a problem arises in that the screw can not be sufficiantly retracted to disengage from the encircling groove of the steering column, so that the steering wheel can not be pulled off from the steering column. As the screw head is not to project outwards over the steering wheel covering, it can not be gripped, unless a large recess is provided in the steering wheel covering, which likewise is not desired.
The present invention provides an improved steering wheel with a fastening screw forming part of a structural unit, consisting of the steering wheel proper and an airbag module, without a requirement for a separate component for final installation such as a separate nut, thereby facilitation the mounting and dismounting procedures.
According to the invention, a steering wheel for vehicles is provided which comprises a hub for attachment on a steering column and a clamping screw. The hub has a central, substantially cylindrical passage for accommodation of an end section of the steering column and at least one slit extending parallel to the passage. Two hub sections are defined on opposite sides of the slit. The hub sections have aligned bores that extend substantially tangentially to the passage. A first one of the bores has an internal thread, and the clamping screw is adapted to extend through a second one of these bores and to be screwed into the first one of the bores, thereby clamping the hub on the steering column end section. A screw holder is attached to the hub for limited movement in an axial direction of the clamping screw against spring force. The screw holder has a recess for passage of the screw and simultaneous engagement into the thread of the screw. Preferably, the screw holder is formed by a bracket of spring steel, and the clamping screw has a shaft with a screw thread formed on substantially the length of the shaft. In a further preferred embodiment, the clamping screw has an abutment formed by a radially projecting collar on a central part of the shaft.
With the arrangement of a non-rotatable, axially elastically deflectable screw holder the problems initially indicated are removed. The screw holder is arranged so that the screw, on mounting of the steering wheel, must be pushed forward axially against the spring force until its front end engages into the internally threaded bore in one of the hub sections. Thereby, screw holder is axially biased, so that an axial restoring force acts permanently on the screw with the installed steering wheel, even when the screw is screwed forward further. An axial clamping force acts on the screw as long as the screw thread is still in engagement with the inner thread within the corresponding hub section. If the screw thread comes out from the inner thread, the screw is pulled back by the axial spring bias of the screw holder so that it no longer engages tangentially into the encircling groove of the steering column. The abutment collar on the central part of the screw shaft provides for a limitation of screw engagement by abutment on the hub surface. Another purpose of the abutment collar is to limit withdrawl of the clamping screw so that it remains attached to the hub. With the non-rotatable, axially elastically deflectable screw holder for the clamping screw, a solution was found by which the conventional steering wheel structure with two hub sections, able to be tensioned elastically with respect to each other, can be mounted and dismounted in a conceivable simple manner without the provision of additional fastening means.